ptpd: update to version 2.3.1-rc2

Add a little processing to find correct directory
for source upstream.

Update LIC_FILES_CHKSUM since the latest package
doesn't include a COPYRIGHT file anymore.

Signed-off-by: Joe Slater <jslater@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Joe MacDonald <joe_macdonald@mentor.com>